The invention relates to means for selectively over-riding the pressure-responsive operative range of a constant-pressure fluid discharge nozzle, such as used in fire fighting.
Such constant-pressure fluid discharge nozzles are structured to maintain a substantially uniform reach of the fluid discharge stream by maintaining a constant fluid discharge pressure, within the operative gallonage range of the nozzle, despite variations in the supply pressure or supply volume of fluid, which may occur for various reasons.
Examples of such constant pressure nozzles can be found in Allenbaugh, U.S. Pat. Nos. 3,904,125; 4,172,559 and 4,289,277; McMillan, U.S. Pat. No. 3,863,844, and Burnam et al, U.S. Pat. No. 2,568,429.
All of these prior art patents use a yieldably-mounted pressure-responsive baffle to progressively enlarge the nozzle discharge orifice or opening as fluid pressure or volume in the nozzle increases. The enlargement of the orifice permits a greater volume of fluid discharge to relieve the increased pressure in the nozzle and thereby maintain constancy of discharge pressure and, correspondingly, a uniform reach of stream.
During operation of the nozzle, the baffle may move from a minimum flow position to a maximum flow position, as defined by the length of permissible longitudinal displacement or stroke of the baffle assembly in the specific nozzle structure. Within these limits, the baffle is free to move in response to fluid pressure fluctuations and hunt for an equilibrium position for maintaining uniformity of fluid discharge pressure. The prior art constant-pressure nozzles are not intended to and do not provide any means for selectively fixing the orifice opening at selected gallonage positions. There are prior art fixed gallonage nozzle structures which utilize some means, usually manual rotation of the nozzle sleeve, to selectively enlarge or reduce the size of the orifice to control discharge flow.
There are, however, circumstances where the wholly automatic flow control characteristic of the constant-pressure nozzle creates undesirable consequences. For example, every nozzle operator has to fight the reaction of the nozzle, particularly at flows of 100 g.p.m. and more, when two operators are often required. This reaction force is based upon a formula of volume times the square root of the fluid pressure. Therefore, an abrupt increase in pump supply pressure to the nozzle results in significantly increased volume and suddenly increased reaction force at the nozzle, which a single operator may be unable to handle or control.
Such an abrupt increase in supply pressure may occur, for example, when there are several hose lines in use and, without warning, some are shut down, thus diverting greater flow pressures and volumes to the remaining line or lines, each of which were readily controlled by a single nozzle operator when all the lines were being used. The sudden increase in the nozzle reaction force could cause the operator to lose control of the nozzle at a critical time in the fire-fighting operation, and could even cause injury to the operator before assistance could arrive.
When using an adjustable fixed gallonage type of nozzle, an operator can adjust the orifice to a gallonage setting which he can handle safely, and not fear a sudden increase in reaction force. In the constant-pressure type of nozzle, the operator does not have this option, and is vulnerable to sudden reaction force increases.